Up to now, as a circuit which is driven by a single power source, that is, one positive power source and outputs a signal to a small resistor terminated at the ground, Patent document 1 discloses a technology for a charge pump circuit which drives a video amplifier as illustrated in FIG. 13. In this conventional technology, the charge pump circuit generates a negative power source (VEE) based on a positive power source (VCC) and a ground voltage (GND), and a driven circuit which is driven between the positive power source (VCC) and the negative power source (VEE) directly drives a load without using a capacitor for cutting a DC (direct current) with the ground voltage (GND) being as a central level, whereby a signal is outputted.
In the charge pump circuit used in this technology, during a first period of a clock signal, a capacitor is directly connected between a supplied positive voltage and the ground voltage to accumulate electric charges, and during a second period of the clock signal, the capacitor is directly connected between the ground voltage and a negative voltage terminal which generates a negative voltage to transfer the accumulated electric charges. This series of operations is repeatedly performed, to thereby generate the negative voltage.
In such a charge pump circuit, during the period during which the electric charges are accumulated in the capacitor, a current amount is large during the earlier half of the period, gradually decreases with time, and becomes smaller during the latter half of the period. When the amount of the current consumed by the video amplifier and the load thereof is large, the large current flowing during the earlier half of the period causes problems such as power source noise and consumption beyond the current supply capability.
As a technology for solving these problems, Patent document 2 discloses a technology for a charge pump circuit which drives a video amplifier as illustrated in FIG. 14. According to this technology, the current amount during the period during which the electric charges are accumulated in the capacitor of the charge pump circuit is set to be constant. In this technology, a constant current is generated by using an internal constant current circuit irrespective of the amount of the current consumed by the video amplifier, and this constant current is used for accumulating the electric charges in the capacitor. Therefore, the equivalent amounts of currents flow between the earlier half and the latter half of the period during which the electric charges are accumulated, and hence it is possible to prevent the large current from flowing only during the earlier half of the period.